#include <iostream>
#include <iomanip>
using namespace std;

int main(int argc, char **argv)
{
	double sum = 0;
	for (int i = 1; i <= 12; ++i)
	{
		double a;
		cin >> a;
		sum += a;
	}
	sum /= 12;
	cout << "$" << setiosflags(ios::fixed) << setprecision(2) << sum << endl;
	return 0;
}
